Electrochemical energy storage devices such as batteries are becoming increasingly important to the rapid development of a wide variety of technologies ranging from small neural stimulators to electric vehicles. Addressing the power demands of these devices requires attention to a variety of performance factors. Although each application has a differing set of priorities almost all have the same set of needs. These include greater gravimetric and volumetric energy density, lower cost, an increase in the ease of cell fabrication, and improved safety. For the past two decades, Li-ion technology has been the premiere battery technology and has evolved little since its first introduction. In this technology, both the positive and negative electrodes operate on the basis of intercalation reactions where guest ions insert into a stable crystalline host structure. For the positive electrode, this host structure typically has been layered (LiCoO2) or three dimensional (LiMn2O4) host metal oxide structures. The positive electrode is the energy limiting electrode of the Li-ion battery. Therefore attention to the improvement of this electrode is key to the improvement of the energy density of the battery. Existing and proposed intercalation materials are limited to the insertion of one lithium and one electron per formula unit; it is imperative for improved energy density that this limitation is extended well beyond one electron and one ion. Recently a concept of conversion materials has been introduced in order to set a stage where two or three electrons can be transferred per transition metal thereby increasing the energy density of the battery by at least a factor of two (see Poizot, P, et al., Nature. 2000 Sep. 28; 407(6803):496-9, the entire content of which is incorporated herein by reference). The most proficient conversion materials in this respect have been the class of metal fluoride nanocomposites (see U.S. Ser. No. 11/813,309; PCT/US06/00448; U.S. 60/727,471; U.S. 60/641,449; Bervas, M., et al., J. Electrochem. Soc. 2006. 153(4):A799-A808; Bervas, M., et al., Electrochem. Solid-State Lett. 2005. 8(4):A179-A183; Bervas, M., et al., J. Electrochem. Soc. 2006. 153(1):A159-A170; Badway, F., et al., J. Electrochem. Soc. 2003. 150(10):A1318-A1327; Badway, F., et al., J. Electrochem. Soc. 2003. 150(9):A1209-A1218; Badway, F., et al., Chem. Mater. 2007. 19:4129-4141; Pereira, N., J. Electrochem. Soc. 2009. 156(6):A407-A416; Amatucci, G. G., and Pereira, N., J. Fluorine Chem. 2007. 128:243-262; the contents of each of which are incorporated by reference herein in their entirety). During the discharge or lithiation reaction, the metal fluorides are reduced to the metal and LiF in a sub-nanocomposite of dimensions <5 nm. The metal fluoride material is reformed during the subsequent charge or delithiation. This can be performed many times over, thus affording rechargeability to the technology. The metal fluorides themselves are insulators, but such appreciable electrochemical activity is made possible by the formation of nanocomposites, which enable the electrochemical activity of the materials.
In many instances, a self formed battery based on fluoride electrodes would be of interest and offers many important attributes. For example, without limitation, the use of a self formed battery would lower the fabrication cost considerably as there would not be any costs associated with individual electrode fabrication. Another example is that as an indefinite reserve battery, at the time of need, the cell would be formed into the highly reactive electrodes that normally would exhibit some degradation if left in storage for long periods of time. Another example is that the cell would be very easy to form into small or conformal dimensions as only one layer of fluoride material would have to be deposited. As another example of high importance, the use of a self formed battery technology would enable the use of metal halide electrodes of exceptional voltage and energy density but extreme reactivity to the ambient environment and poor process stability. Forming such materials in-situ would eliminate the extreme difficulty of handling unstable materials, potential toxicity and especially high cost of fabricating these materials ex-situ. In short the self-formed electrochemical cell is utilized as a chemical factory itself. An example of the impact of this invention can be seen in the theoretical energy density of the successful incorporation of this concept to the in-situ formed Li/Ag—AgF2 couple. This cell energy density would exceed 3500 Wh/L, which is greater than 3× of today's state of the art Li-ion technology.
The described invention relates to electrochemically formed metal halide batteries and provides compositions and examples of a metal fluoride cell in which one of the components is a known glass former. In a further embodiment, the battery may operate through a bi-ion energy storage mechanism where, upon the formation of the battery, a cation and anion, for example Li+ and F−, diffuse to opposing reactive current collectors to form the cell in situ.